Effective earthing safeguards people from risk of
electric shock, that ‘hazardous-live-parts shall
not accessible and accessible conductive parts
shall not hazardous live’, and ensures low
impedance route the general mass earth for
currents the electrical system, under both
normal and fault conditions. Extending
the earthing arrangement through the use of
equipotential bonding measures cover
exposed and conductive metal parts further
recommended protect against step and touch
voltages, and remove risk dangerous
sparking.
Performance requirements for earthing these low
voltage installations are defined the IET Wiring
Regulations, 7671. Five classes low voltage electrical
installation are defined within the standard
- TN-S, TN-C, TN-C-S, and IT.
A number national and international standards
have been published which define earthing
system design parameters for structures,
electrical equipment and systems, including:
• 50522: Earthing power installations
• exceeding 1kVac
• 7430: Code practice for protective
earthing electrical installations
• 7354: Code practice for design high
voltage open terminal stations
• IEEE Std 80: IEEE Guide for safety AC
• substation grounding
• ENA 41-24 Guidelines for the design,
installation, testing and maintenance main
earthing systems substations
The design, specification, inspection and periodic
testing earthing systems should follow the
guidance and recommendations provided by
these standards.—
Technical reference
Earthing standards
Installation well designed earthing system is
a fundamental requirement for all structures and
electrical systems (at all voltages).
The earthing arrangement should sufficiently
robust ensure lasts the lifetime the
installation, and protected from mechanical
damage and corrosion that remains capable
of carrying the maximum expected current, for
which specified, under both normal and
fault conditions.
118 FURSE® EARTHING LIGHTNING PROTECTION
QUALIT SOLUTIONS FOR SAFEGUARDING PEOPLE, STRUCTURES AND SERVICES
.
BS 7430: Protective earthing electrical
installations
British Standard 7430 provides guidance on
earthing general land-based electrical
installations and around buildings the UK,
and considers:
• Low voltage installation earthing and
equipotential bonding for general, industrial
and commercial buildings, locations with
increased risk, rail systems etc
• The interface between low voltage and high
voltage substations
• Earthing generators and Uninterruptible
Power Supplies (UPSs) supplying low voltage
installations
BS 7430 defines the elements for creating an
appropriate earthing arrangement for low
voltage installation, including main earthing
terminal, protective conductors, earthing
conductors and circuit protective conductors,
and the use earth electrodes dissipate
currents the general mass earth
